The present invention relates to a robot apparatus, and more particularly to a robot apparatus including tracks along the X-, Y-, and Z-axes of a Cartesian coordinate system, the robot apparatus being designed to prevent the tracks from interfering with each other and thereby increasing the working area or envelope of the robot itself and have being capable of continuous use for a long period of time.
Recent years have seen widespread use of robot apparatus which automatically perform verious operations for mass-production and have higher efficiency. One good example of such robot apparatus is an automatic line production system having an array of robots of one type of different types.
Some of such robot apparatus have drive mechanisms displaceable in the three directions of the X-, Y-, and Z-axes of a Cartesian coodinate system for a larger working envelope so that they can effect various steps of an operation. Japanese Laid-Open Patent Publication No. 57-21290, for example, discloses a conventional robot apparatus that is displaceable in the directions of such three axes.
The disclosed conventional robot apparatus is illustrated in FIG. 1 of the accompanying drawings. The robot apparatus includes a support post 2 supporting, on its upper end portion, two arms 4a, 4b which extend in different directions. On the arms 4a, 4b, there is supported a horizontal X-axis rail unit 6 with an X-axis drive mechanism 8 secured to one end thereof. A cable 10, which may be a wire, is trained around the X-axis drive mechanism 8 and a pulley 7 rotatably mounted on the other end of the X-axis rail unit 6, the cable 10 being coupled to an X-axis slider 12 movable on and along the X-axis rail unit 6. The X-axis slider 12 has a Z-axis drive mechanism 14 to which there is secured a Z-axis rail unit 16 extending vertically in perpendicular relation to the X-axis rail unit 6. A cable 18, which may be a wire, is trained around a pair of pulleys 17 rotatably mounted on the opposite ends of the Z-axis rail unit 16. The cable 18 is also trained around the Z-axis drive mechanism 14 and connected to a Z-axis slider 20 movable on and along the Z-axis rail unit 16. The Z-axis slider 20 has a Y-axis drive mechanism 22. A horizontal Y-axis rail unit 24 has one end fixed to the Z-axis slider 20 and extends substantially perpendicularly to the X-rail unit 6 and the Z-axis rail unit 16. A Y-axis slider 26 is movably mounted on the Y-axis rail unit 24 and coupled to a cable 28, which may be a wire, trained around the Y-axis drive mechanism 22 and a pulley 27 rotatably mounted on the other end of the Y-axis rail unit 24. A chuck device or a holder 30 for holding a workpiece (not shown) is mounted on the Y-axis slider 26.
Operation of the robot apparatus thus constructed is as follows: When the X-axis drive mechanism 8 is driven, the cable 10 is moved thereby to displace the X-axis slider 12 horizontally along the X-axis rail unit 6 in the X-axis direction. When the cable 18 is moved by the Z-axis drive mechanism 14, the Z-axis slider 20 is displaced vertically along the Z-axis rail unit 16 in the Z-axis direction. Movement of the cable 28 caused by the Y-axis drive mechanism 22 enables the Y-axis slider 26 to move horizontally along the Y-axis rail unit 24 in the Y-axis direction until the holder 30 reaches a desired position in which a workpiece (not shown) is located.
After the workpiece is gripped by the holder 30, the X-axis drive mechanism 8, the Y-axis drive mechanism 22, and the Z-axis drive mechanism 14 are driven to move the workpiece to a desired position.
With the aforesaid prior arrangement, the holder 30 can be moved by the drive mechanisms 8, 22, 14 in any desired direction in the Cartesian coordinate system having X-, Y-, and Z-axes. However, as is readily understood from FIG. 1, since the Z-axis rail unit 16 is fixed to the X-axis slider 12 and extends vertically, the Z-rail unit 16 is required to move in the X-axis direction when the holder 30 is moved in the X-axis direction. This leads to a problem in that the space required for the Z-rail unit 16 to move in is quite large, limiting the space area in which to move the workpiece in the Y-axis direction. As a result, the directions in which to move the workpiece or the positions in which to install the robot apparatus are limited, and smaller working spaces cannot accommodate the robot apparatus. The sliders are moved by the cables or wires. Therefore, the cables are apt to be elongated and worn in use, and have to be replaced periodically to meet desired accuracy requirements. For this reason, the robot apparatus cannot be operated continuously for a long period of time, and hence cannot perform automated tasks efficiently.
Another known robot apparatus is disclosed in Japanese Laid-Open Patent Publication No. 57-194891. According to this prior robot apparatus, a rail unit extending along one of the three axes of a Cartesian coordinate system, for example, an X-axis rail unit extending in the X-axis direction, is secured to a fixed table, and an X-axis movable body is mounted by a rack and pinion on the X-axis rail unit. A holder body is secured to the X-axis movable body, and a Z-axis movable arm is mounted by a rack and pinion on the holder body for movement vertically in the Z-axis direction. To the upper end of the Z-axis movable arm, there is fixed another holder body mounting thereon a Y-axis movable arm through a rack and pinion, the Y-axis movable arm being movable in the Y-axis direction. A measuring or gripping head is mounted on one end of the Y-axis movable arm.
The measuring or gripping head can be moved in the directions of the three coordinate axes by moving the X-axis movable body, the Z-axis movable arm, and the Y-axis movable arm through the respective rack and pinions.
However, when the head is to be moved vertically in the Z-axis direction, the Y-axis movable arm extending in the Y-axis direction is also required to be moved in the Z-axis direction. Therefore, as with the prior art robot apparatus shown in FIG. 1, the space taken up by the robot apparatus for moving the head is of a substantially size.
U.S. Pat. No. 4,005,782 discloses still another conventional robot apparatus. A Y-axis movable body movable by a cylinder is mounted on a guide rod extending in the Y-axis direction in a Cartesian coordinate system. Another guide rod extending in the X-axis direction has one end secured to the Y-axis movable body, and an X-axis movable body movable by a cylinder is connected to the guide rod. A cylinder oriented vertically in the Z-axis direction is fixed to the X-axis movable body. A Z-axis movable body is coupled to a rod extending vertically downwardly from the cylinder fixed to the X-axis movable body. A hand is openably and closably mounted on the Z-axis movable body.
This prior-art robot apparatus is advantageous in that since no guide rod extends in the Z-axis direction, a workpiece gripped by the hand can be moved easily in any desired direction.
The Y-axis movable body, the X-axis movable body, and the Z-axis movable body are movable in the Y-axis, X-axis, and Z-axis directions respectively by their cylinders. If the ranges of movement of these movable bodies are to be increased for moving various different workpieces, then the cylinders have to be increased in length, and hence the robot apparatus results in a larger size.
Another prior robot apparatus is shown in U.S. Pat. No. 4,229,136. A first holder that is vertically movable by a first motor is mounted on a Z-axis arm extending vertically in the Z-axis direction, and a cylinder mechanism for vertically moving a tool or the like is coupled to the first holder. A second holder having a second motor is secured to the first holder. An Y-axis arm extending in the Y-axis direction and movable in the Y-axis direction by the second motor is fitted in the second holder. A third holder is secured to an end of the Y-axis arm. An X-axis arm fitted in the third holder is movable in the X-axis direction by a third motor fixed to the third holder. A gripping tool, for example, is mounted on an end of the X-axis arm.
The tool can be vertically moved highly smoothly by driving the cylinder mechanism in a manner to meet the weight of the tool that is mounted on the X-axis arm.
However, since the Z-axis arm extends vertically in the Z-axis direction and the Y-axis arm, the X-axis arm, and the tool are supported on the Z-axis arm, the range in which the tool can be moved is substantially limited as with the prior art illustrated in FIG. 1.
According to a still further prior robot apparatus disclosed in U.S. Pat. No. 4,260,319, a support post is erected vertically in the Z-axis direction, and an articulated arm which is extensible and contractable by a weight adjusting means is coupled to an upper portion of the support post. A bar extending vertically downwardly is secured to an end of the articulated arm. An X-axis rail member extending in the X-axis direction through a guide is supported on the support post, and an X-axis movable member is movably mounted on the X-axis rail member through a drive means such as a wire or a rack and pinion. To the X-axis movable member, there is fixed an end of a Y-axis rail member extending in the Y-axis direction. A Y-axis movable member is movably mounted on the Y-axis rail member through a drive means. The Y-axis movable member is fitted over the rod coupled to the articulated arm for guiding the rod in a desired direction.
With the above prior robot apparatus, the rod can be moved in vertical orientation (in the Z-axis direction) at all times through the Y-axis movable member. Therefore, by holding a workpiece with a hand mounted on the lower end of the rod and driving the X-axis and Y-axis movable members in the X-axis and Y-axis directions, respectively, the workpiece can be fed accurately and quickly to a desired position.
When the rod is guided by the Y-axis movable member to move in the X-axis and Y-axis directions, however, the articulated arm is extended, contracted, and turned under the operation of the weight adjusting means. For moving the hand on the rod in the Z-axis direction at different positions in the X-axis and Y-axis directions in response to the operation of a driver of the weight adjusting means, the control of the driver is quite complex because of different attitudes of the articulated arm at such different positions in the X-axis and Y-axis directions. In addition, the vertical space occupied by the robot apparatus is large inasmuch as the articulated arm connected to the support post extends upwardly substantially beyond the X-axis and Y-axis rail members. As a consequence, the robot apparatus cannot be installed in smaller working spaces.